Transcript Chapter11-Nuclear En..

Nuclear Energy
Fossil Fuel vs. Nuclear Fuel
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Fossil Fuel: Provides energy by
chemical reactions (No change in
atoms)
Uranium: There is a change in
structure of atom (energy release I
given in terms of binding energies)
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Atom
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Atomic Number = # of protons
(P)
Mass Number =# neutrons +
protons (A=n+P)
The nucleus of an atom of
carbon has 6 protons and 8
neutrons
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Binding Energy per Nucleon
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Fission (breaking up the heavy atoms)
Fusion (fusing the light atoms)
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Isotopes
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Isotopes are unstable atoms having the same
number of protons, but different number of
neutrons (different A and same P).
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U-235 has 92 protons and 143 neutrons, U-236 has 92
protons and 144 neutrons. Normal hydrogen has 1
proton and 0 neutron, deuterium has 1 proton and 1
neutron, tritium has 1 proton and 2 neutrons
Nomenclature
( number of protons) 92
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U235 (atomic mass number)
Isotopes
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Isotopes are chemically identical but
physically are very different
Isotopes are radioactive
Isotopes are rare
234
92 U
235
92 U
238
92 U
1
1H
2
1H
3
1H
(0.006%)
(0.714%)
(99.28%)
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(99.80%)
(0.15%)
(0.05%)
Fission
History
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1896 – Antone Bequerel (France)
uranium salt darkened photographic plates even in total dark
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1900 – Maria Curie (Poland)
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1911 - Ernest Rutherford (New Zealand)
radioactivity consisted of three components
first planetary model of atom of hydrogen
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1945 - First atomic explosion
Alamogordo, New Mexico, July 16
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1945 – Fist Atomic Bomb
Hiroshima, August 6
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U.S. Nuclear Industry
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103 Power plants as of 1996 providing
20 % of the US electric power
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90% are in Northeast and Midwest
Oil Embargo – 1973
No new plants since - 1976
Accident at Three Miles Island - 1979
Operating licenses for many power plants will
expire in the next ten years.
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Nuclear Plants
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Fission
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Basic Physics
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Reactions
U-235 + n  U-236
Many ways that U-236 can decompose, e.g.
 U-236  Ba-137 + Kr-97 + 2n + energy
 U-236  Xe-140 + Sr-94 + 2n + energy
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Energy is in the form of gamma-rays
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Nuclear Energy
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Energy E= Dm. C2
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Nuclear energy from 1-kg of uranium =
Chemical energy from 2000 tons (2 million
kg) of coal
Mass is usually expressed as atomic mass
unit
1 amu= 1/12 of the mass of C-12 atom=1.66x10-7
kg
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Uranium
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Uranium ore is only .7% U-235, rest is U-238
U-235 must be enriched to 3% before it can be used
as nuclear fuel.
 Only U-235 is fissionable (fertile). If neutron not
acquired by U-235, it will be acquired by U-238
 The slower the neutron, the more chance that U235 will acquire it.
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Fuel Cycle
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Nuclear Power Plant
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Basic Components
of Conventional Nuclear Reactors
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Fuel Rods (3% U-235, 97% U-238)
Control Rods (Boron/ Cadmium)
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Moderator (Graphite / Water)
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B-10 + n  Li-7 + He-4
If neutron is too fast  short contact time
If neutron is too slow not enough energy
Coolant (Water / Sodium)
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Types of Reactors
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Coolant
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Moderators
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Water, Graphite
Pressure
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LW, HW, Gas, Liquid Metals
Low Pressure (LWR)
Pressurized (BWR)
Fuel
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Uranium-235
Plutonium-239
MOX
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Classification
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Light Water Reactors
Pressurized Water Reactors
Boiling Water Reactors
High Temperature Gas Cooled Reactors
Fast Breeder Reactors
Pebble Bed Modular Reactors
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Breeder Reactors
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Convert Non-fissionable U-238 to fissionable
Pu-239
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Can use either U-235 or Pu-239
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U-238 + n  Np-239  Pu-239
Mainly in Europe and Russia
Must use sodium (instead of water) as
coolant/moderator
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Does not slow down neutron (as water does)
Much higher heat capacity
Disadvantages are:
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Sodium is highly explosive
Plutonium is bomb-grade quality
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Breeder Reactors
238U + n  239U  239Np  239Pu
uranium-238 + neutron  plutonium-239
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Pebble Bed Reactors
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Nuclear Safety
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Nuclear Regulatory Commission is in charge
of all nuclear safety issues
Major factors are:
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Design
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Steel-reinforced containment must withstand severe hurricanes
and earthquakes, and direct hit by a large jetliner
Multiple backup systems must be in place
Automatic shutdown in case of loss of coolant
Training
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TMI accident was attributed to deficient personnel training
Clear operating procedures
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Three Miles Island
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Near meltdown in March 28, 1979
Over 3 billion dollars in cleaning costs
Two million people (within 50 miles
radius) were exposed to low level
radiation (no statistical way of
determining how many will die from
cancer)
Nuclear Industry created a watchdog
agency, Institute for Nuclear Power
Operation (INPO)
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(Harrisburg, PA)
Chernobyl, Ukraine
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April 26, 1986 explosion followed by fire in reactor#4
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Fire extinguished by dropping 5000 tons of sand and boron.
Eventually encased in 300,000 tons of concrete.
Remaining Chernobyl reactors decommissioned in 1999.
Why?
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RBK-1000 design unstable at low powers
Poor training
Inadequate containment
Reactor was used as a research facility as well as power production
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Chernobyl – Consequences
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8000 have already died. No estimate on the ultimate death toll
from the accident
160,000 people were forced to leave their homes
1500 acres of surrounding forest died instantly; 5 million acres
of prime farmland were contaminated; 20% of farmland and
15% of the Belarus forests cannot be used over 100 years.
Rate of thyroid cancer in Ukrainian children have climbed 30fold.
Higher rate of spontaneous abortion by Belarusian women
Wild life is blooming. Field mice are undergoing evolutionary
changes that took other species 10 million years.
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Nuclear Fusion
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Hydrogen Isotopes
Abundance:
Normal
99.8%
Deuterium
.015%
Tritium
.005%
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Fusion vs. Fission
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Fusion:
D + T  He + n + energy
(DE=4x1011 BTU/kg deuterium)
Fission
U + n  Kr + Ba +3n + energy
(DE=7x1010 BTU/kg U-235)
Coal (recall)
C+O2  CO2+ energy (DE=3.3x104 BTU/kg coal)
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Fusion
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Fusion Reactions
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D+D
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@ 400 million oC
He-3 + 3.3 MeV (79 MJ/g)
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D+T
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@ 45 million oC
He-4 + 17.6 MeV (331 MJ/g)
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Breakeven Point
Where plasma can be raised at
sufficiently high temperature and
particle density, and long enough
so the rate of energy production
exceeds the rate of energy required
for sustained reaction.
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Challenges
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Ignition
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Very high temperatures to overcome
repulsive forces of positively charged nuclei
Confinement
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Very high pressures to increase probability
of collision
And for times long enough for producing
energy more than that required for heating
and compression (sustained reaction)
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Confinement
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No solid vessel
Magnetic confinement
Inertial confinement (laser)
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Magnetic Confinement
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